1. Field of the Invention
The present invention relates to a chalcopyrite structure semiconductor thin film containing a specific dopant and a process of producing the same.
2. Description of the Related Art
The chalcopyrite structure semiconductor is a material useful for constituting light-emitting devices and solar cells, because its forbidden band can be wide from a visual region to an infrared ray region and it has a large optical absorption coefficient due to the constituent elements. It is indispensable to produce a p-n junction in manufacturing the solar cells or light-emitting devices. For controlling p-n conductivity type of the chalcopyrite thin film, a method of changing the composition ratio between a Group I element and a Group III element or between a Group II element and a Group IV element which are the constituent elements of chalcopyrite compounds has been used conventionally. For example, in the case of CuInSe.sub.2 thin film, n-type conductivity is formed when the proportion of the Group III element Cu is less than that of the Group I element In, and in the opposite case p-type conductivity is formed. In these cases, a problem is encountered in that many lattice defects occur due to deviations in the composition ratio. There are also such problems as deposition of excessive amounts of components or the appearance of an impurity phase other than the chalcopyrite structure. R. Noufi et al., also report that, it is difficult to control carrier concentration and resistivity by changing the composition ratio (Appl. Phys. Lett., 45 (1984) p.688). Particularly, most of the chalcopyrite semiconductor thin films which take on n-type conductivity by deviation of the composition ratio shows a high resistance, and thus a low resistance film is not obtainable.
In fabricating the p-n junction by using the chalcopyrite thin film produced by the prior art, such inconveniences as lattice defects and depositions of excess components owing to deviations of composition ratio, or the formation of an impurity phase other than the chalcopyrite-structure appears as mentioned before. As a consequence, the electrical and optical characteristics of the chalcopyrite thin film are deteriorated. Thus, when devices having a p-n junction are manufactured by using the chalcopyrite thin film produced by the prior art, the efficiency of the devices is inferior due to the deterioration of electrical and optical characteristics. For example, because of an increase of carrier recombination centers due to the lattice defects and the impurity phase, the open-circuit voltage of the solar cell decreases and also the quantum efficiency of semiconductor laser decreases.
When an n-type high resistance film is used, in the solar cells the short-circuit current decreases, and in the light-emitting devices the carrier injection efficiency reduces. Thus, the conversion efficiency of the solar cells and the luminous efficiency of the light-emitting devices are deteriorated.
Moreover, in the solar cells, the depletion layer of the p-n junction must be broadened to convert incident light efficiently into electrical energy. Thus it is necessary to control the carrier concentration.